When a boat or other vessel is moored to a pier or other mooring by means of a wire rope or other flexible but relatively inelastic line, it is conventional to provide the line with some type of device for maintaining the line taut while allowing a predetermined amount of resilient elongation in order to allow relative movement between the vessel and its mooring.
U.S. Pat. No. 4,022,450, entitled "Line Tensioning Device," is representative of one such prior art device which utilizes a pair of tension springs to maintain a resilient Z-shaped bend in the line that stretches into a more elongated shape when a predetermined tensile force is applied to the line.
U.S. Pat. Nos. 546,788 and 869,130, respectively, entitled "Cable Buffer" and "Yielding Boat Cleat", disclose prior art mechanical devices in which one or more coil springs are compressed as excessive tensions or strains are applied to the hawser, cable or rope.
U.S. Pat. Nos. 143,993 and 107,917, respectively entitled "Windlasses" and "Improvements in Surge-Relievers" disclose other devices in which shocks in the cable caused by the movement of the vessel are absorbed by a plurality of rubber springs.
It will be noted that the above-described prior art tension absorbing devices utilize spring elements which are compressed or elongated in a linear direction and accordingly there is an approximately linear relationship between the stress applied to the rope and the resultant increase in its effective length.
U.S. Pat. No. 4,273,066, entitled "Oil Storage Vessel, Mooring Apparatus and Oil Delivery for the Off-Shore Production of Oil," proposes various apparatus for mooring a vessel at sea to a deep water submerged mooring which includes both a mooring line (which depending upon the particular application may be either a floating rope or a heavy chain) and a flexible length of oil transfer hose. The Patent makes mention of a manually or automatically controlled tension releasing (self-rendering) mooring winch, and a mechanical damping device (a damping roller) at columns 5 and 8. Column 15 of the Patent describes a mechanism called "The Damper" which is said to be designed and adjusted to absorb a portion of the shock cyclical loadings placed on the mooring line. The Damper is described as comprising a concave roller with butt ends over which the mooring line will pass, the roller being held at a specific height above and astern of the wire rope winch by two arms which pivot about an axis, the arms in turn being held in position by springs or hydraulically controlled arms. This same Patent also discusses the use of a mooring line to effect a resilient connection between a floating storage vessel and a service tanker with the required tension being provided by placing the propeller on the service tanker in its reverse power position to provide a predetermined amount of tension on the line and the oil hose is arranged in such a way that a relative motion between the vessels of up to a 150 feet (about 45 meters) may be accommodated (column 12).
Mechanical tensioners have also been employed to maintain a more or less constant tension in endless drive belts such as are utilized to drive the various accessory subsystems associated with a modern automotive engine. Such belt tensioner devices are intended to compensate for the changes in the belt's length during its service lifetime while ensuring that a proper amount of tension is maintained in the belt to eliminate any slipping between the belt and the various pulleys around which it travels and at the same time without exerting an excessive tension force on the belt.
U.S. Pat. No. 4,285,676 and Reissue Pat. No. 30,842, entitled respectively "Mechanical Belt Tensioner Construction" and "Tensioning Apparatus," disclose typical prior art endless drive belt tensioners wherein a torsional spring is provided at one end of a lever arm for pivotally moving an idle pulley at the other end of the lever arm in a direction generally perpendicular to the belt's longitudinal orientation as it extends between adjacent fixed pulleys to thus compensate for changes in the belt's length by increasing the effective distance between the fixed pulleys. The torsional spring may comprise a plurality of coil springs (such as is shown in U.S. Pat. No. 4,285,676) or, alternatively, may be a hollow cylinder of elastomer material which exerts the required rotational force as the result of the elastomer being subjected to a torsional shear (such as is shown in Reissue No. 30,842).
U.S. Pat. No. 3,817,113, entitled "Chain Drive with Idler Wheel Tensioning Means Biased by Elongated Pads," is particularly related to a chain drive for textile machines which may have to be abruptly stopped and restarted such that the chain thereby experiences considerable strain. A torsion effect results as a plurality of rubber pads are distorted in cross section as the tension device is rotated.
It will be appreciated that dampers that have been adapted for use with continuous belt chains and other similar drive systems will never be required to handle the particularly large forces and constant pounding that are associated with many nautical applications. Accordingly, the reactive force resulting from the application of an unbalanced torque (rather than a balanced torque couple) will probably not materially affect the reliability of such device when used for their intended application.
U.S. Pat. No. 2,087,253, entitled "Tilting Mechanism Especially for Chairs," illustrates the use of a cylindrical body of rubber that is highly compressed and confined between concentric tubular members so as to in effect be bonded to their surfaces such that relative rotary movement between the tubular members puts the rubber body under torsional strain. An adjusting mechanism is provided to vary the torsional strain imposed upon the rubber and thus the force required to tilt the seat of a chair supported by such a resilient rubber arrangement. Such a form of construction is believed to be exemplary of a number of different applications in which a cylindrical rubber bushing is utilized to accommodate a limited rotational movement between adjacent structural elements, while at the same time biasing the mechanism to its normal position. It should be noted that such a bushing, although cylindrical in shape, does not employ what is hereinafter referred to as "longitudinal torsional shear" and that furthermore the "radiating" torsional shear within the rubber is concentrated in its hub portion, rather than being distributed uniformly.